Thin NaCl films on silver (001): island growth and work function

Abstract

The surface work function (WF) and substrate temperature dependence of the NaCl thin-film growth on Ag(001) have been studied by noncontact atomic force microscopy and Kelvin probe force microscopy. In the sub-monolayer range, the NaCl film is composed of large crystalline islands, which decrease in density and increase in size with increasing temperature during deposition. Each island is composed of a large base island 2 monolayers (ML) thick (for T > 343 K), which collects impinging NaCl molecules that form adislands on top. Kelvin probe force microscopy (KPFM) measurements show a reduction of the silver WF by ϕ = ϕ Ag − ϕ NaCl/Ag = 0.69 ± 0.03 eV with no dependence on the film thickness (1-6 ML), in agreement with recent theoretical calculations. The previously observed nanometer-sized moiré pattern on islands that are 45 • rotated with respect to the silver lattice could be observed in the scanning tunneling microscopy mode. However, no contrast could be obtained in KPFM images.

Reaction kinetics of ultrathin NaCl films on Ag(001) upon electron irradiation

“…The island edges exhibit various orientations with respect to the substrate axes, in agreement with previously reported azimuthal mosaicity [39,41,42]. After longer deposition times (30 min instead of 10 min) at the same cell temperature, NaCl films reveal similar features with larger side lengths, in the 200-500 nm range (data not shown here).…”

“…[40]) and comparison with previous STM [38] and noncontact atomic force microscopy [39] studies. Cabailh et al [39] observed that NaCl films grown on Ag(001) at substrate temperatures in the 343-443 K range essentially consist of 2 ML-thick islands. At low bias voltage (U b = 1 V), in the area shown in Fig.…”

“…Thin NaCl films are grown on a single crystal of Ag(001). High substrate temperatures of 413 and 500 K increase the NaCl molecule diffusion on silver during the deposition to obtain larger NaCl domains [38,39]. Two different substrate temperatures, used for the NaCl growth, yield different film geometries, as shown below.…”

“…The local thickness of the NaCl domains, i.e., the number of atomic monolayers (ML), is determined from the apparent height measured by STM at different bias voltages [43,44] (see STM height profiles in Ref. [40]) and comparison with previous STM [38] and noncontact atomic force microscopy [39] studies. Cabailh et al [39] observed that NaCl films grown on Ag(001) at substrate temperatures in the 343-443 K range essentially consist of 2 ML-thick islands.…”

Atomic Structures of Silicene Layers Grown on Ag(111): Scanning Tunneling Microscopy and Noncontact Atomic Force Microscopy Observations

“…If in the course of such experiments the bias voltage is varied as an additional parameter, very important electronic properties of the silicene films could be extracted as well, as it has been exemplified on the Si(111)(7 × 7) surface32. Such experiments could be further assisted by Kelvin probe microscopy33, which has shown to be quite powerful for measuring, e.g., work function differences at the nanometer34 and even atomic scale35. Most importantly, since STM as well as nc-AFM nowadays allow manipulating atoms36, molecules37 and clusters38, the two types of microscopes could be used, in principle, to manipulate the second layer silicene islands on the first one, provided that the coupling between the layers is only weak.…”